Navigate flying molecular elephants safely to the ground: mass-selective soft landing up to the Mega-Dalton range by Electrospray Controlled Ion-Beam Deposition

28 September 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The prototype of a highly versatile and efficient preparative mass spectrometry system used for the deposition of molecules in ultra-high vacuum (UHV) is presented, along with encouraging performance data obtained on four model species which are thermolabile or not sublimable. The test panel comprises two small organic compounds, a protein, and a large DNA species covering a 4-log mass range up to 1.7 MDa as part of a broad spectrum of analyte species evaluated to date. Three designs of innovative ion guides, a novel digital mass-selective quadrupole (dQMS) and a standard electrospray ionization (ESI) source are combined to an integrated device, abbreviated Electrospray Controlled Ion Beam Deposition (ES-CIBD). Full control is achieved by i) the square-wave-driven radiofrequency (RF) ion guides with steadily tunable frequencies, including a dQMS allowing for investigation, purification and deposition of a virtually unlimited m/z range, ii) the adjustable landing energy of ions down to ~2 eV/z enabling integrity-preserving soft-landing, iii) the deposition in UHV with high ion beam intensity (up to 3 nA) limiting contaminations and deposition time, and iv) direct coverage control via the deposited charge. The maximum resolution of R=650 and overall efficiency up to T_total=4.4% calculated from solution to UHV deposition are remarkable as well, while the latter is mainly limited by the not yet optimized ionization performance. In the setup presented, a scanning tunneling microscope (STM) is attached for in situ UHV investigation of the deponents demonstrating a selective, structure-preserving process and atomically clean layers.

Keywords

soft-landing
ion beam deposition
native organic molecule
preparative mass spectrometry
electrospray ionization
nano-architecture
scanning tunneling microscopy
ultra-high mass range
digital quadrupole
ion guide
surface science
mega-Dalton
self assembly
bio-molecule
DNA
insulin
porphyrin

Supplementary materials

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Title
Navigate flying molecular elephants safely to the ground: mass-selective soft landing up to the Mega-Dalton range by Electrospray Controlled Ion-Beam Deposition - Supplementing Info
Description
Instrumental settings and parameters (section 1-2); calculation of insulin adducts (section 3); calculation of cylindrical Rayleigh limit (section 4); overall efficiency benchmarking (section 5); typical CIBD-parameters for Rhodamine B (section 6); experimental details and references (section 7-9)
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